The present invention relates generally to lubrication systems for engines, and more particularly, to a lubrication system for the upper valve mechanism of an overhead valve engine.
Horizontal crankshaft engines generally include breather induced upper valve mechanism lubrication systems, wherein the breather is located on top of the rocker box, and where an oil mist is induced to flow upwardly by the breather from the crankcase through both push rod tubes to the rocker box chamber to lubricate the valve actuating mechanism in the rocker box. Oil which condenses in the rocker box is then drained back downwardly along the side walls of the push rod tubes to the crankcase.
In vertical crankshaft engines, the above-described breather induced lubrication system does not perform satisfactorily due to several problems. First of all, when the engine is oriented in the head down attitude, oil will not drain from the rocker box to the oil sump, thus causing oil to build up in the rocker box. As enough oil builds up, the breather will pump oil from the rocker box to the exterior of the engine. However, this is unsatisfactory because of oil spillage on and around the engine and the loss of lubricating oil which can result in engine failure due to lack of lubrication.
It has been proposed to use a scavenging pump to remove the liquid oil from the rocker box and thereby prevent the build up of liquid oil therein. However, the provision of such a pump adds to the cost of the engine which is unsatisfactory.
More recently, a lubrication system has been developed, wherein the breather is remote from the rocker box, and the system utilizes crankcase breather induction of oil mist in a counter flow through two separate push rod tubes with the feeder push rod tube directly connected to the engine crankcase and the return push rod tube connected to the engine breather box which vents through a breather mechanism to the atmosphere. This lubrication system causes oil mist from the crankcase to flow up one push rod tube, circulate within the cylinder head rocker box to lubricate the valve mechanism, and then be induced by the crankcase breather into the breather box where a liquid oil is separated from the vapors. The liquid oil drains back into the crankcase, and the vapors are vented to the atmosphere through the remote breather mechanism. Such a system is shown in U.S. Pat. No. 4,601,267.
Another recently developed lubrication system provides lubrication to the upper valve mechanism without requiring the use of breather induction. This system employs a centrifugal oil slinger in the crankcase, which slings oil through a push rod cavity that is in communication with the crankcase at one end and in communication with the rocker box at the other end. The rocker arms in the rocker box are disposed one above the other, each oriented for rocking in a substantially horizontal plane. A dam is provided for restraining oil slung into the rocker box at a level such that the lower rocker arm is partially submerged in a pool of liquid oil. The turbulence of the lower rocker arm and valve spring generates enough turbulence in the accumulated pool to cause splash lubrication onto the upper rocker arm and its associated valve assembly. Such a lubrication system is shown in U.S. Pat. No. 4,881,496.